Computing technology continues it long term trend of becoming less expensive while providing more capability in terms of speed, storage density, and display pixel density. However, this trend may not continue. To allow computing technology to continue to provide more capability, peripheral devices such as mass storage devices and display devices must continue to advance. Hard disk drives, for example, have been able to increase the storage density tremendously over the last decade but are now encountering physical limitations that prevent further progress in density. Moreover, criticism has been voiced in the trade press about the inability of manufacturers of mass storage devices (such as disk drives, CD-ROMs, and DVD drives) to increase the data rate inline with the advancing speed of the microprocessors thereby limiting the system performance of such electronic devices as personal computers. In addition, although some hard disk drives have been miniaturized to operate with portable devices, their high power requirements still limit long-term battery operation. A higher data rate, more energy efficient, and high-density storage device is needed.
Users continue to insist on higher density display devices such as LCD panels and cathode ray tubes. Increasing the pixel resolution requires faster data rates to the display device because the display must be refreshed at the same rate as previous low density displays in order to prevent unwanted display flicker. In addition, display devices, such as LCD monitors have had difficulty in fulfilling demand due to the complexity of manufacturing them with near-zero defects. Further, the use of passive LCD technology has required the addition of backlights to allow for viewing in different ambient light conditions. These backlights require additional power thereby further limiting long-term battery operation.
Cathode ray electron beam technology has been present for many years in consumer products such as television (TV) tubes and computer monitors. These devices use what is known as xe2x80x98hot cathodexe2x80x99 electrodes to create a source of electrons that are directed to and focused on the viewing screen. While research has taken place in a number of new technological fields, the field of xe2x80x98cold cathodexe2x80x99 electron emitters such as Spindt-tips and flat emitters has attracted the attention of many manufacturers.
Several problems exist in converting this cold cathode technology into useful products. In general, electron beams need to: deliver sufficient current; be efficient; operate at application-specific low voltages; be focusable; be reliable at required power densities; and be stable both spatially and temporally at a reasonable vacuum for any given application. It has been difficult to achieve high current density, stability and reliability in one cold cathode architecture. For instance, a conventional flat tunneling emitter was reported to have an emission current density of only 0.1 to 1.00 mA/centimeter squared with an efficiency of less than 0.1 percent.
For example, while Spindt tips can provide both spatial and temporal stability and reliability, they can only do so while in a relatively strong vacuum greater than that of outer space thereby making their practical use difficult to achieve. Further, a Spindt tip is relatively difficult to focus compared to flat emitters.
One problem in creating stable and reliable flat emitters is that manufacturing defects or slight deviations in film thickness can easily cause damage to the emission surface due to xe2x80x9cbeetle galleryxe2x80x9d formations once the emitter is operated at high emission levels. For instance, metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) tunneling emitters tend to have much higher flickering and beetle gallery defects when operating at high emission levels. The beetle gallery defects tend to reduce the lifetime of the devices by causing fast aging and ultimate failure (usually shorts) of the device as this effect shifts from one emission center on the emitter surface to another as the emission sites fail.
If these problems persist, it will be unpractical to use cold cathode technology in multiple applications that require high speed, low power, and a high density of emitting devices such as with mass storage and display devices used in electronic devices.
An emitter includes an electron source and a cathode. The cathode has an emissive surface. The emitter further includes a continuous anisotropic conductivity layer disposed between the electron source and the emissive surface of the cathode. The anisotropic conductivity layer preferably has high conductivity emission sites distributed within a low conductivity layer to provide for substantially uniform emissions of all emission sites over the emissive surface of the emitter.